1. Field of the Invention
The present invention relates to an image sensor, and particularly relates to an image sensor which can read image data from read regions with different shapes and apply a buffer with reduced size.
2. Description of the Prior Art
FIG. 1 is a schematic diagram illustrating a prior art optical touch control apparatus. As shown in FIG. 1, the optical touch control apparatus 100 comprises a touch control panel 101, an image sensor 102, light guiding devices 105, 109 with bar shapes and photo diodes 103, 107, 111, 113. The light guiding devices 105, 109 are provided at two sides of the touch control panel 101. The photo diodes 103, 107, 111, 113 are respectively provided at the endings of the light guiding devices 105, 109, to project light to the touch control panel 101 via the light guiding devices 105, 109. The image sensor 102 is provided opposite to the light guiding devices 105, 109. If an object Ob (ex. user's finger) moves on the touch control panel 101, the image sensor 102 can sense the projection image for the object image Ob, which means the dark region generated via shading light from the light guiding devices 105, 109 by the object Ob. The location for the object Ob is computed accordingly.
The image sensor 102 can comprise a pixel array 120 and an image data reading circuit 122, as shown in FIG. 2 and FIG. 3. The data reading circuit 120 senses the image and generates the image data. The image data reading circuit 122 reads the image data generated by the pixel array 120. Please refer to FIG. 2, which illustrates a projection image for an ideal object track on the image sensor 102 in FIG. 1. The ideal state here means no error or skew occurs when the touch control panel 101 and the image sensor 102 are fabricated. In such case, the light guiding devices 105, 109 present a rectangular bright background on the pixel array 120 as shown in FIG. 2. The movement for the object on the touch control panel generates dark region to the bright background, therefore the bright background can be regarded as a possible moving track for the object Ob. However, practically the product has assembly tolerance, such that the error or skew may occurs when the touch control panel 101 and the image sensor 102 are fabricated. In such case, the moving track Obt′ for the object Ob on the pixel array 120 is an oblique parallelogram as shown in FIG. 3.
The image data reading circuit 122 always reads the data of the pixel array 120 row by row or column by column. Therefore, the example in FIG. 2 only needs to read image data of the pixel rows in the moving track Obt to acquire the location of the object Ob. However, the example in FIG. 3 needs to read image data of all pixel rows or all pixel columns to acquire the image data for all pixels in the moving track Obt′ to acquire the location of the object Ob. In such case the image data reading circuit 122 needs much time to read the image data.
In some systems, a frame buffer is provided for the image sensor for buffering image data until image data for a whole frame is received. A size for a conventional frame buffer is always equal to a size of a frame, which is equal to a size of the sensing matrix. In one example, a sensing matrix has a size of 150 pixels×1024 pixels, that is, the sensing matrix comprises 150 rows×1024 columns, in such case a size of a conventional frame buffer is 150 rows×1024 columns.
However, in above-mentioned cases, only image data for the read region, which is smaller than the whole sensing matrix, is read. Accordingly, much space of the conventional frame buffer is wasted.